Assertion : Cross Cannizzaro's reaction between methanal and benzaldehyde gives benzyl alcohol and formate ion.
Reason : Benzaldehyde does not contain a-hydrogen atom.

Answer

To solve the given assertion and reason question, we need to analyze both the assertion and the reason separately.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states: "Cross Cannizzaro's reaction between methanal and benzaldehyde gives benzyl alcohol and formate ion."
- In a Cross Cannizzaro reaction, one aldehyde that lacks an α-hydrogen reacts with another aldehyde that has α-hydrogens. Methanal (formaldehyde) has α-hydrogens, while benzaldehyde does not.
- The products of the Cross Cannizzaro reaction involving methanal and benzaldehyde would typically yield benzyl alcohol and formic acid (not formate ion).
- Therefore, the assertion is **incorrect** because it states that the products are benzyl alcohol and formate ion, which is not accurate.

2. **Understanding the Reason**:
- The reason states: "Benzaldehyde does not contain an α-hydrogen atom."
- Benzaldehyde (C₆H₅CHO) has no α-hydrogens because the carbon adjacent to the carbonyl group (the carbonyl carbon) is part of the aromatic ring and does not have any hydrogen atoms attached to it.
- Therefore, this statement is **correct**.

3. **Conclusion**:
- The assertion is incorrect, while the reason is correct. In logical terms, a correct reason does not validate an incorrect assertion. Hence, the correct answer to the question is that the assertion is false, but the reason is true.

### Final Answer:
- The assertion is incorrect, and the reason is correct. Thus, the correct option is **C**.